Heretofore it has been well known that aircraft wheel assemblies are subjected to significant static and dynamic forces. While the wheels are static while the aircraft is in the air, immediately upon touchdown, the wheels necessarily spin up to high rotational speeds while being subjected to significant side, radial, and drag forces while the aircraft is maneuvered through its braking and taxiing operations. Accordingly, the wheel bearings for aircraft wheel assemblies must necessarily accommodate such forces and force variations.
Wheel bearing failures have generally not been existent in the past and, accordingly, have not been of great concern. However, recent attention in the aircraft industry to the possibilities of wheel bearing failures have given rise to considerations for testing wheel bearings in a manner to replicate their use in the field.
Presently in the art, only rudimentary attempts have been made to devise aircraft wheel bearing test systems. Such attempts have fallen far short of replicating the wheel assembly of an aircraft and/or the operating environment and characteristics of the associated bearings. One known system is that shown in U.S. Pat. No. 4,862,738. However, in such systems the true environment of the wheel bearings is not replicated, for the test systems fail to generate all of those forces typically applied to an aircraft wheel in operation.
Applicants have found that the true replication of an aircraft wheel assembly during operation requires that the axle assembly be fixed, that the forces to be coupled to the bearing must be imparted to the wheel, not the axle, and that the forces include radial forces, side forces, and the drag forces which result from fore and aft loads on the aircraft itself. Accordingly, to fully synthesize or replicate an aircraft environment, these forces must be available and must be variable to replicate wheel spin up at landing and the characteristic loads and speeds on the wheels during all ground operations.